Field
This disclosure relates to an organic light-emitting device.
Description of the Related Technology
Organic light-emitting devices (OLEDs), which are self-emitting devices, have advantageous characteristics such as wide viewing angles, excellent contrast, quick response, high brightness, excellent driving voltage characteristics, and can provide multicolored images.
A typical OLED has a structure including a substrate, and an anode, a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and a cathode which are sequentially stacked on the substrate. In this regard, the HTL, the EML, and the ETL are organic thin films formed of organic compounds.
An operating principle of an OLED having the above-described structure is as follows.
When a voltage is applied between the anode and the cathode, holes injected from the anode move to the EML via the HTL, and electrons injected from the cathode move to the EML via the ETL. The holes and electrons recombine in the EML to generate excitons. When the excitons drop from an excited state to a ground state, light is emitted.
A major factor that affects the emission efficiency of an OLED is its light-emitting material. Fluorescent materials are widely used as light-emitting materials, and it is also an effective method for emission efficiency improvement to use phosphorescent materials that are capable of improving emission efficiency up to four times based on theoretical electroluminescence mechanisms. Iridium (III) complex-based phosphorescent materials such as (acac)Ir(btp)2, Ir(ppy)3, and Firpic may be used for red, green, and blue emission, respectively.

4,4′-N,N′-dicarbazole-biphenyl (CBP) is one example of known phosphorescent host materials.
Although advantageous in terms of light-emitting characteristics existing light-emitting materials may have a low glass transition temperature and poor thermal stability, and thus may be deteriorated during a high-temperature deposition process under vacuum. According to the relationship that “power efficiency=(π/voltage)×current efficiency”, i.e., the power efficiency of an OLED is in inverse proportion to a voltage, the power efficiency of the OLED may be increased to lower consumption power of the OLED. In practice, an OLED using a common phosphorescent (host) material such as BAlq or CBP may have a considerably higher current efficiency (cd/A), but also have a higher driving voltage, as compared with an OLED using a fluorescent material, and thus is not advantageous in terms of power efficiency (lm/w).

OLEDs using such an existing host material are also not satisfactory in terms of lifetime, and thus there is a need to develop a more stable host material with improved characteristics.